I. Field of the Invention
This invention relates to dies for forming the helical threads on a metal fastener and, in particular, to thread rolling dies which prevent laps and discontinuities in the thread form during manufacture of the fastener.
II. Description of the Prior Art
Thread rolling dies have been used for many years to form the helical threads on a fastener which allows it to be threadably received within an aperture. In typical manufacturing, the fastener blank is formed to the desired length and diameter. The blank has a substantially smooth outer circumference. In order to form the threads in the blank, the blank is positioned between a pair of grooved dies. While one of the dies is kept stationary, the other die is moved longitudinally thereby rolling the blank along the dies. The grooves of the dies form the desired threads in the shank of the fastener as it moves across the dies. The grooves of the die are formed according to the desired depth and angle of the finished threads. In addition, the rolling dies must be configured to the diameter of the fastener blank.
While the use of standard thread rolling dies to form the threads works well for most fastener manufacturing, the use of such dies for fasteners causes laps in the thread form resulting in considerable scrap. The fastener blank can slip between the dies causing defective threads. The known thread rolling die geometry has been an obstacle to the mass production of lap free fasteners. Accordingly, a thread-rolling technique and a process of configuring thread dies which would produce defect-free threads while maintaining mass production rates is desired.